The present invention relates to compression spring rods such as a spring and rod assembly that exerts an expansional force which increases at a linear rate. The compression spring rods embodying the present invention are useful in motor vehicles for easing the opening of closure members such as luggage compartment lids, engine compartment lids, hatchbacks, doors, etc; however, the springs can be used in applications other than for vehicles (e.g., garage doors, windows, etc.). The present invention is still more particularly directed to springs having a rod member to exert the driving force on the elements to be displaced.
Compression spring rods are used in various applications, for example, to assist in lifting, opening, and damping. Typical applications include lifting a lid hinged to a stationary base. Other applications include lifting and/or balancing elements for the trunk or hatchback of an automobile. Still another application includes a damping spring for closing a door hinged to a stationary frame. Most applications involve the use of a pneumatic or gas spring to assist the opening motion. Many of these types of compression spring assemblies contain either gas or hydraulic fluid to control forces and piston speeds. Consequently, because these products contain a gas and/or fluid, they are subject to premature failure, due to the leakage of the gas or fluid over time. The leakage results in a loss of control forces and a subsequent loss of spring life. Two types of prior art gas springs are disclosed in U.S. Pat. Nos. 5,887,857 and 6,179,099, both of which are incorporated herein by reference.
In an effort to overcome the past deficiencies of springs, a spring system having multiple springs was developed as disclosed in U.S. patent application Ser. No. 10/056,941 filed Jan. 28, 2002. The multiple spring system was designed so as to produce a linear load versus deflection curve. Although the multiple spring system is a significant improvement over past spring configurations, the rate at which the multiple spring system was compressed or expanded was essentially dependent on the load applied to the multiple spring system. In some applications, the rate at which a spring system is compressed or expanded may need to be altered in certain application to inhibit or prevent overly rapid compression or expansion of the spring system. In view of the present state of the art, there remains need for a spring system that overcomes the past problems with gas spring systems and also which controls the rate of compression and/or expansion of the spring system.